In the past semiconductor devices of integrated circuits were typically formed in a silicon substrate. As silicon devices such as transistors and diodes have become smaller, the frequency of operation for the integrated circuits has increased. This increase in frequency, and the decrease in the space separating devices has resulted in increased potential interference between adjacent semiconductor devices. For example, a current going through one device may result in a leakage of current to an adjacent device, which can disrupt the function of the adjacent device.
In order to reduce the potential for interference between neighboring devices in an integrated circuit, one common approach is to use shallow trench isolation techniques to form isolation trenches between adjacent devices. This technique requires the etching of trenches in the substrate and the forming of an insulting material such as an oxide, or a nitride, in the trench. In these prior approaches the trench is relatively shallow as compared with the substrate. Thus, it is possible for some electrical current to propagate under the bottom of the trench to an adjacent device, and to cause interference with the adjacent device.
Another prior technique provides for forming silicon semiconductor devices in a trench formed in an insulating layer formed on a silicon substrate. One such process is described in U.S. Pat. No. 6,225,666, issued May 1, 2001, entitled LOW STRESS ACTIVE AREA SILICON ISLAND STRUCTURE WITH NON-RECTANGULAR CROSS-SECTION PROFILE AND METHOD FOR ITS FORMATION, which is hereby incorporated by reference in its entirety. As shown in FIG. 1, hereto, the process described in the '666 patent provides for using different etching techniques to etch a trench having wine glass shaped lateral sides 110 in an insulating layer 104 formed on a silicon substrate 102. After the trench has been formed in the insulating layer an active silicon area 108 is formed on an exposed area 106 of the substrate 102, using an epitaxial process. Semiconductor devices can then be formed in the active silicon area 108 formed in the trench. This approach, however, requires both dry etching step and wet etching steps, which are then followed by an epitaxial process for forming an active silicon area 108 on the substrate 102. The process of forming the trench in the insulating layer and forming the active silicon area on the silicon substrate can increase the time associated with fabricating the semiconductor devices of the integrated circuits.